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Stainless Steels Classifications
Stainless steels are commonly grouped
into martensitic stainless steels, ferritic stainless steels,
austenitic stainless steels, duplex (ferritic-austenitic) stainless
steels, and precipitation-hardening stainless steels
Stainless steels are in general grouped
- martensitic stainless steels
- ferritic stainless steels
- austenitic stainless steels
- duplex (ferritic-austenitic) stainless steels
- precipitation-hardening stainless steels
Alloying metallic elements added during
the making of the steel increase corrosion resistance, hardness,
or strength. The metals used most commonly as alloying elements
in stainless steel include chromium, nickel, and molybdenum.
Stainless steels are available in the
Stainless steels are a iron-based alloy
containing at between 10.5% to 30% Cr. Stainless steel
achieve its stainless characteristic through the formation of
an invisible and adherent chromium-rich oxide surface film.
Other alloying elements added to improve
the characteristics of the stainless steel include nickel, molybdenum,
copper, titanium, aluminum, silicon, niobium, nitrogen, sulphur,
Carbon is normally in amounts from
0.03% to more than 1.0% in some martensitic grades.
Selection of stainless steels are in
general based on
- corrosion resistance
- fabrication characteristics
- mechanical properties for specific temperature
- product cost
Since stainless steel resists corrosion,
maintains its strength at high temperatures, and is easily maintained,
it is widely used in items such as automotive and food processing
products, as well as medical and health equipment. The most common
US grades of stainless steel are:
The most commonly specified austenitic
(chromium-nickel stainless class) stainless steel, accounting
for more than half of the stainless steel produced in the world.
This grade withstands ordinary corrosion in architecture, is durable
in typical food processing environments, and resists most chemicals.
Type 304 is available in virtually all product forms and finishes.
Austenitic (chromium-nickel stainless
class) stainless steel containing 2%-3% molybdenum (whereas 304
has none). The inclusion of molybdenum gives 316 greater resistance
to various forms of deterioration.
Ferritic (plain chromium stainless
category) stainless steel suitable for high temperatures. This
grade has the lowest chromium content of all stainless steels
and thus is the least expensive.
The most widely used martensitic (plain
chromium stainless class with exceptional strength) stainless
steel, featuring the high level of strength conferred by the martensitics.
It is a low-cost, heat-treatable grade suitable for non-severe
The most widely used ferritic (plain
chromium stainless category) stainless steel, offering general-purpose
corrosion resistance, often in decorative applications.